Not Applicable
Not Applicable
1. Field of the Invention
The invention pertains generally to methods for determining the position and surface contours of an object and, more particularly, to a method for determining surface coordinates by directing intensity modulated illumination toward the surface of an object and mathematically resolving the reflected intensity pattern into position and distance relative to the modulated illumination, whereupon the object coordinates may then be determined by triangulation.
2. Description of the Background Art
Numerous applications require determining the coordinates of an object""s surface, or the coordinates of reflective elements beneath that surface. Typical application areas include industrial plants, laboratories, microscopy, and the metrology field in general. Various optical methods have been employed which utilize arrangements of light sources to detect contour information. These methods are often employed within instruments such as coordinate measuring machines, three-dimensional topometric sensors, and laser triangulation sensors. One common method of performing surface coordinate measurements is to project a lighted grid of squares onto the surface of an artifact, capture the reflected image on an image sensor, and then analyze the image data. The distortion of the grid within the image may be analyzed to discern the shape of the object. The grid lines may be mapped to ascertain the angles of the beams and the coordinates of the points of intersection. Triangulation is typically utilized during the process of calculating the coordinates of the object points once sufficient angle and position data is obtained.
It will be appreciated that a right triangle can be resolved given any two sides, or an angle and a side. FIG. 1 is a two-dimensional diagram of triangulation being performed to resolve the position of point Pxe2x80x2, wherein a ray of light from a known location and direction P, is reflected from the surface of the object at point Pxe2x80x2 and is detected at a location Pxe2x80x3. A pair of right triangles is formed which may be solved if the distance or additional angular information is given. By solving for the pair of right triangles, the coordinates of points on the surface of the object may then be determined.
Methods of determining object coordinates often rely on a method of scanning the surface of the object point-by-point or line-by-line, and resolving the point positions of the object serially. However, sequential methods of plotting the coordinates of an object surface are slow and not well suited for use on vibrating or moving objects. The coordinates of object points may also be determined by creating interference patterns in the region near the surface using multiple illumination sources, such that the reflected patterns disclose changes in field depth as a series of interference fringes. In another method, predetermined displacements of a projected light grid having a sinusoidal pattern are mechanically generated, as by rotating an aperture. The reflected light from the object is detected by an image sensor so that the response to the angular displacement for the aperture is evaluated by a phase-shift method (or Fourier transform) to determine the incoming angle of the light. The object location is then solved by triangulation. The two grating positions may be generated simultaneously using multiple wavelengths of light, such as colors in the visible spectrum, which are resolved by a detector individually responsive to each of the wavelengths. The utility of this technique and its accuracy are dependent on the surface characteristics of the object and require substantial precision with regard to the gratings and their rotation.
The aforementioned methods of determining the coordinates of an object surface suffer from a number of drawbacks, such as being typically slow, while many of the methods inherently lack mathematical precision. Therefore, a need exists for an efficient method of determining object position under a variety of conditions and which does not rely on image distortion, sequential scanning, interference patterns, or pixel position rotations. The present invention satisfies those needs, as well as others, and overcomes the deficiencies of previously developed solutions.
The present invention is directed to a method for determining the three-dimensional coordinates of points located on the surface of an object. By way of example, and not of limitation, a light source, an optical intensity modulator, two lens systems, and a charge coupled device camera having a large number of optically sensitive pixels, are positioned in such a manner that the illumination is directed through the intensity modulator and the first lens system onto the surface of the object from which it is reflected through the second lens system onto the camera. The intensity modulator preferably comprises a liquid crystal window having a plurality of pixels whose transmittance qualities are independently adjustable from opaque to transparent. The illumination passing through the intensity modulator is modulated according to at least three mathematical relationships of pixel position. Calculations are performed on the illumination received at the pixels of the camera to resolve the distance and position of the associated pixels at the intensity modulator. The location of coordinates on the object from which the illumination is reflected may then be determined based on well known triangulation calculations.
Accordingly, the invention is a simplified method for determining the location of the points on the surface of an object by varying, in accord with mathematical formulas, the intensity of illuminated pixels directed to the object surface, and performing calculations on the intensity of reflected illumination in relation with the mathematical formulas to resolve the coordinates of the object surface
An object of the invention is to optically determine the absolute position of points on an object by varying the intensity of illumination projected onto the object.
Another object of the invention is to provide a convenient method for the simultaneous registration of reflected pixels over an area of the object illuminate by a modulated beam so as to speed the process of coordinate mapping.
Another object of the invention is to provide a method for mapping the surface coordinates of an object without the need of complex equipment.
Another object of the invention is to provide a method for rapidly resolving the surface coordinates of an object.
Another object of the invention is to provide a method of determining the coordinates of an object without the use of rotating illumination grids.
Another object of the invention is to provide a method of mapping the surface coordinates of an object that may be implemented with available low-cost components.
Further objects and advantages of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.